Solubilization of indomethacin by polysorbate 80 in mixed water-sorbitol solvents

The effect of indomethacin on the micellar properties of the non-ionic surfactant, polysorbate 80, in water-sorbitol mixtures containing up to 25% w/v sorbitol has been investigated by light scattering, photon correlation spectroscopy and viscometric techniques. The molecular weight of polysorbate 80 micelles containing solubilized indomethacin increased linearly with increase of sorbitol concentration. Solubilization of indomethacin resulted in an increase of micellar weight due not only to the incorporation of solubilizate but also to an increase in the number of polysorbate molecules per micelle. The micelles in all systems were most satisfactorily represented as oblate ellipsoids, the asymmetry and hydration of which increased with increase of sorbitol concentration. Indomethacin solubilization caused a restructuring of the micelle to produce a more symmetrical micelle of increased hydration.